The present invention relates to determining the state-of-health (SOH) of an electrochemical device. More particularly, the present invention relates to determining the SOH of a lead-acid battery of the type used in portable defibrillators using an intelligent system, e.g. a fuzzy logic system.
The SOH of a battery, fuel cell, or other electrochemical device has been interpreted in different ways by scientists/engineers in the field. In the case of valve regulated lead acid (VRLA) batteries used by utility companies for providing emergency backup power, SOH is interpreted to mean that a battery is close to the end of its cycle life and needs replacement. Several papers including Feder and Hlavac 1994 INTELEC Conf. Proc. pp. 282-291 (1994) and Hawkins and Hand 1996 INTELEC Conf. Proc. pp. 640-645 (1996) demonstrate that the increase in impedance of aging VRLA batteries can be used to indicate the SOH of the battery.
Another interpretation of battery SOH is the capability of a battery to meet its load demand. This is also referred to as xe2x80x9cbattery conditionxe2x80x9d by others in the field. To obtain the SOH of a battery in the terms defined, both the available charge capacity of the battery and the maximum power available from the battery are required. Several approaches have been used to determine the condition of a battery. In U.S. Pat. No. 5,365,453 is described a method in which a ratio of a change in battery voltage to a change in load is used to predict impending battery failure in battery powered electronic devices. Similar methods in which the battery response to and recovery from the application of a load is used to determine the SOH of batteries are reported in U.S. Pat. Nos. 4,080,560 and 5,159,272. While these load profiling approaches work reasonably well for batteries integrated into a system, they are not necessarily accurate or reliable ways of determining the SOH of batteries outside a system.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a method of and system for determining the state-of-health of a lead acid battery of the type commonly used in portable external defibrillators, the method comprising detecting an impedance characteristic of the battery at at least one selected frequency, counting the number of complete charge/discharge cycles that the battery undergoes, and determining the state of health of the battery from a fuzzy system trained in a relationship between the impedance characteristic and the cycle number of the lead acid battery and the state-of-health, wherein the state-of-health is a function of and varies with the battery""s ability to deliver power required by the load and the battery""s capacity to meet load requirements.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.